Various fabrications of heat-insulating joints of pre-insulated pipelines are known. For example, patent for invention GB2319316, published on May 20, 1998, IPC F16L 59/20, discloses one such fabrication. This fabrication includes joining the pipelines' ends to each other, installing a polymeric coupling on the joint with its ends covering the ends of polymeric jackets of the pipelines, welding the coupling's longitudinal weld, joining the coupling with the ends of jackets of the pipelines to be coupled, checking for tightness of the coupling and jackets, and filling the space between the inner and outer surface of the coupling. The outer surface of the joined pipelines and ends of the pipeline include heat insulation with heat-insulating material.
Another method for joining isolated metal pipes is disclosed by patent for invention GB1483143, published on Aug. 17, 1977, IPC F16L 59/20. According to this reference, two metal pipes, each of which has a hose made of insulating material such as rigid polyurethane foam, and end lugs at a distance from the pipe edge are welded and insulated with an additional heat-insulating material. The heat-insulating material includes two half sections, which are disposed around the weld. The hoses include heat-shrinkable plastic material that is placed on the additional heat-insulating material and on a portion of a bush that is connected to each pipe. The bush is heated to capture the insulating material. Optionally, the sealing bush made of material used for the hose is installed over the end of the insulation on the pipe before installing the bush, and the welded joint is covered with anticorrosive coating prior to application of an additional insulating material.
Another method for sealing the joint between two insulated pipes is disclosed by patent for invention EP0079702, published on May 14, 1986, IPC F16L 59/20. According to this reference, water and heat insulation of welded joints of pipes is made using heat-shrinkable materials and heat-insulating pipe coverings. The outer joint between the pipeline and the housing, that covers the heat-insulating pipe coverings, is further protected with heat-shrinkable material. The polymeric material is coated with a sealant, such as mastic, and heat-activated adhesive, such as hot melt adhesive. The coated material forms a bush which can have a tubular or circular configuration. The sealant provides a flexible waterproof seal around the welded joint, and the adhesive provides a second seal and prevents any movement of the hose and the pipe.
Another method of providing an anticorrosive insulation of welded joints of a pipeline and a device for its implementation are disclosed by patent for invention RU2398155, published on Aug. 10, 2012, IPC F16L 13/02. According to this reference, a heat-shrinkable coupling is first placed on the pipeline near a joint before welding the pipeline ends. After the joints have been welded, the surface to be insulated is cleaned with metal brushes, drained from moisture, and coated with a primer and mastic tape, which is a coating with softening mastic material temperature of 80-90° C. Afterwards, the heat-shrinkable coupling is shifted, mounted in the area of the welded joint symmetrically to the joint, and heated to shrinkage temperature of 110-120° C. The mastic tape layers are heated and melted through the heat-shrinkable coupling to ensure simultaneous pressure on the molten mastic of the mastic tape to use it for filling the cavities in the area of the welded joint reinforcement (tent areas) and the places of transition to the base coating and overlapping layers of the mastic tape.
A heat-insulating joint of pre-insulated pipelines is disclosed by patent for invention RU2235246, published on May 20, 2010, IPC F16L 59/18). The heat-insulating joint of pre-insulated pipelines is interconnected by welding and includes a metal housing, wrapped around the joint and arranged symmetrically to the joint center. The joint also includes polyurethane foam filling the space between the inner surface of the metal housing, the outer surface of interconnected pipelines and the ends of the heat-insulating material of these pipelines. A polymeric coating is used as a heat-shrinkable fabric with an adhesive layer superimposed on the metal housing. The heat-shrinkable polymeric coating is connected with its ends covering the low-pressure polyethylene envelopes. The metal housing has a filling orifice and a conical plug. The heat-insulating joint of pre-insulated pipelines is implemented as follows. A metal housing is mounted symmetrically to the joint center by wrapping it around the joint. The space between the inner surface of the housing, the outer surface of interconnected pipelines and the ends of the heat-insulating materials of these pipelines is filled with polyurethane foam. After that the surface of the metal housing in the joint area is activated by heating it with a gas burner flame of 90-100° C. The polyethylene envelope and metal housing are covered with an applicator made of heat-shrinkable fabric and heated to the sweating temperature, then the surface of the metal housing is re-activated in the area of joint to a temperature of 90-100° C. Next, the temperature of the polyethylene envelope and the metal housing is maintained and the adhesive layer is heated by a gas-burner and gradually covered with heat-shrinkable fabric with little effort applied on the joint upwards. The overlapping edges are placed at 11 and 13 hours on a clock face and oriented from downward. The overlapping area of the heat-shrinkable fabric is laid with the heated inner surface of the locking plate, and the fabric is heat-shrunk by heating with a soft burner flame. Furthermore, the edge of the polyethylene envelope and heat-shrinkable fabric is laid with the inner surface of the applicator heated by a gas burner to a sweating temperature. The metal housing is fixed with two binding bands one on each end. The space of the joint to be insulated is filled with polyurethane foam through a hole in the metal housing. After filling the insulated space of the joint with polyurethane foam, the filling orifice is covered with a lid, which is fixed by means of a previously prepared binding band, leaving the gap between the housing and the lid less than 1 mm for air to exit.
However, this method cannot be applied in field conditions in a climate having low ambient temperatures that reach minus 60° C., such as in the installation of heat insulation of pipelines joints in the Far North in wintertime. This is because such methods require maintaining a constant positive ambient temperature while pouring polyurethane foam in the area of joint and a positive pipe temperature for the polyurethane foaming.